1. Field of the Invention
The invention relates to an apparatus for recording and reproducing a digital audio signal and, more particularly, to a recording and reproducing apparatus for a digital audio disc such as a Compact Disc or the like.
2. Description of Background Information
In digital audio recording mediums such as Compact Disc (hereinafter, referred to as CD), Mini Disc (hereinafter, referred to as MD), or the like, a standard is widely used, which has a performance wherein frequency band ranges from 0 Hz to 20 kHz, the number of quantization bits is equal to 16 bits, and the audio channels are two channels.
On the other hand, it has been considered that the human ear can perceive the sound within a range from 20 Hz to 20 kHz. Therefore, the conventional CD satisfying the above performances is regarded to be satisfactory as a recording medium for audio apparatuses. However, in recent studies it is reported that the human ear has the capability of perceiving sounds having frequencies of 20 kHz and higher than 20 kHz. Accordingly, it is becoming required that the audio reproducing capability of the CD allows the reproduction of sounds having the frequency of 20 kHz or higher. When a higher sound quality is pursued, lack of sufficient dynamic range in the audio reproduction by the conventional CD is recognized, and revision of the number of quantization bits is now under consideration. Furthermore, in the current trend of audio systems, the sound field reproduction allows the production of a "presence" like that in a movie theater or a concert hall in a home listening room. To satisfy such a demand, there is proposed a method in which signals for such a sound field reproduction is also recorded on the CD in addition to the signals of two audio channels.
As a reference which satisfies such requirements, it is considered to establish a new CD standard (hereinafter, referred to as Super CD) which satisfies performance wherein the frequency response band lies within a range from 0 Hz to 40 kHz, the number of quantization bits is 20 bits, and the audio channels are four channels. A reproducing apparatus for the Super CD having above standards, however, will have a complicated circuit construction as compared with that of the apparatus designed for the conventional standard (the frequency band lies within a range from 0 Hz to 20 kHz, the number of quantization bits is 16 bits, and the audio channels are two channels), so that such a reproducing apparatus will become expensive. If the above standard of the Super CD is adopted as a general standard, it will compel users who doesn't require a high sound quality to purchase such an expensive reproducing apparatus with a high sound quality. This makes an obstacle for the generalization of the Super CD standard.